Throttle Full Close Switch: Description and Operation

The idle switch and throttle valve potentiometer are used to indicate the position of the throttle valve to the ECU. The ECU uses the signals from these devices, compared with signals from other sensors, to calculate engine load and ignition timing, and to determine when to engage certain functions, such as acceleration enrichment, full throttle enrichment, deceleration fuel cut-off, and idle speed control.

Idle Switch And Throttle Valve Potentiometer (Before March 1990):

Idle Switch And Throttle Valve Potentiometer (After March 1990):

On early 1990 models (produced before March 1990), the idle switch was a separate device with its own harness connector and was mounted on the throttle body next to the potentiometer. On later models (produced after March 1990), the idle switch and throttle valve potentiometer were incorporated into a single unit, but the idle switch still has its own harness connector.

SELF DIAGNOSIS-THROTTLE VALVE POTENTIOMETER
The ECU can recognize an open or short in the potentiometer circuit. The signal from the potentiometer is compared with the signals from the idle switch and the air mass sensor to determine if they agree. If the signals do not agree, or if an open or short circuit is detected, a fault code will be stored.

SELF DIAGNOSIS-IDLE SWITCH
The ECU compares the signal from the idle switch to that of the throttle valve potentiometer and the engine speed sensor, to see if they agree. If the idle switch remains closed during a changing signal from the potentiometer, a fault code will be stored for the idle switch. Also, if the engine speed sensor signal is increasing, indicating "off idle" operation and the idle switch remains closed, or if the idle switch does not close at least once within the first 10 minutes of engine operation, a fault code will be stored for the idle switch.
There is no substitute signal for either the idle switch or throttle valve potentiometer.